Building regulations - new domestic buildings: identification and assessment of energy standard improvements

9. Conclusions

AECOM and Currie and Brown have undertaken a technical, capital expenditure (CAPEX) and a cost impact assessment (CIA) on a range of options for new build dwelling notional performance standards to inform Scottish Government (SG) updates to Section 6 of the Building Standards Domestic Technical Handbook.

The findings of this work have been summarised below. It is recommended that SG consider these findings when making a final decision on the updates to new build Domestic standards.

Following the SG response Building Regulations: Determining the principles for a Scottish equivalent to the Passivhaus standard: Stage 1 consultation the SG is considering how to introduce new minimum environmental design standards for all new-build housing to meet a Scottish equivalent to the Passivhaus standard, in order to improve energy efficiency and thermal performance.

When referencing the Passivhaus standard, the Space Heat Demand is most often considered. However, this forms part of a range of targets which are required to achieve certification. This includes Primary Energy or Primary Energy Renewable (kWh/m²/yr) a representation similar to the Delivered Energy Rate (kWh/m²/yr) currently used by Scottish Building Regulations.

The results of this study similarly highlight the benefit of multiple compliance metrics to ensure that new build dwellings have a balanced specification which reduces fuel consumption and is cost efficient both to construct and operate.

When considering Space Heat Demand alone, the DE technology route appears comparative to the ASHP and DHN technology routes; however, has a significantly different Regulated Fuel Cost. It was highlighted that there are risks around tariff variability that may be challenging to account for in Building Regulations compliance calculations. If applied in combination with Delivered Energy Rate (i.e. having two compliance metrics based on the notional dwelling specification), it is expected that mitigation of high regulated fuel costs is possible. This will may remove the option to apply DE as a heating technology within a dwelling with a high SH demand. The appropriateness of a SH demand target for ASHP heating dwellings may not be required if a Delivered Energy Rate target is applied.

The ASHP is shown to consistently result in the lowest DDER across the archetypes modelled. The DE and DHN are shown to result in a similar DDER across the archetypes modelled; however, DE is shown to have a higher associated regulated fuel cost than the DHN. Further flexibility on the performance specification of new dwellings may be required for DHN heated dwellings. This could be achieved by expanding the delivered energy boundary calculation to include the DHN energy centre efficiency.

For the BAU specification, of the three heating technology options modelled the ASHP has the lowest CAPEX for the houses. This relationship was not observed for the block of flats where the ASHP was the highest for the BAU specification, indicated that ASHP heated flats may not be an effective strategy.

Good and Best Practice specifications achieve improvements to both space heating demand and delivered energy rate metrics for all archetypes. The Best Practice specification was also found to align with the PHPP space heating demand target of 15kWh/m²/yr some of the archetypes assessed (representing circa 40% of the new build housing stock). The CAPEX effectiveness of the Good Practice option was found to be highest; however, it does not achieve the aspiration of aligning with the PH standard.

SG are encouraged to consider the findings of this study and the conclusions drawn when appraising the final options for updating Section 6 of the Domestic Technical Handbook.